Inkjet printing mechanisms may be used in a variety of different products, such as plotters, facsimile machines and inkjet printers, to print images using a colorant, referred to generally herein as “ink.” These inkjet printing mechanisms use inkjet cartridges, often called “pens,” to selectively emit drops of ink onto a page or sheet of print media. Some inkjet print mechanisms carry an ink cartridge, having a supply of ink back and forth across the sheet. Other inkjet print mechanisms, known as “off-axis” systems, propel only a small ink supply with the printhead carriage across the printzone, and store the main ink supply in a stationary reservoir, which is located “off-axis” from the path of printhead travel.
Each pen has a printhead that includes an orifice plate having a number of very small nozzles formed thereon through which ink drops are fired. Traditionally, repeated firing of ink from the nozzles of an orifice plate results in puddling of the ink on the orifice plate. The puddling of inks on the orifice plate of inkjet pens can be an issue for not only general orifice plate cleanliness, but also for the directionality and dot placement on the ink receiving medium since the puddles interfere with ejection of the drops from the nozzles. Problems caused by puddling include drop mis-directionality, massive ink accumulation on the nozzle (orifice) plate, pen service difficulties, and increased ink contact/attack to internal electrical components of the pen.
Typically, ink flow channel design and firing chamber architecture are designed to modulate puddling. Underdamped fluidic architectures enable higher firing frequencies which increase printer throughput, but can lead to increased puddling. Damped fluidic architecture can control puddling by the reduction of ink refill speed. However, damped fluidic architecture may have a negative effect on firing frequency response and ultimately on printer throughput speed. Additionally, damped fluidic architecture is also more susceptible to starvation and camber angle variation from nozzle to nozzle.
Another traditional approach for reducing ink puddling is to increase the viscosity of the ink. This could be realized by adding a high molecular weight surfactant/oligomer/polymer. Using viscous cosolvent or increasing the total organic content can also raise ink viscosity. However, image quality, defined by ink/media interaction, will not be optimized due to the formulation restriction for puddling control and increased ink viscosity generally decreases maximum firing frequency.
Throughout the drawing, identical reference numbers designate similar, but not necessarily identical, elements.